Commercial, industrial, domestic and apartment buildings require ventilation, and it is common for the natural leakage around doors, wall-ceiling joints, etc. found in standard building construction to allow sufficient air to enter the building. A pressure drop from the exterior to the interior of the building can arise from many factors, such as high winds, exhaust fans and combustion air for fuel-burning furnaces. This tends to draw outside air into the building through any crack or opening.
The problem with the conventional approach is that the amount of ventilation air is not controlled, the temperature in the building near the outside walls is lower than average and less comfortable, and additional heat must be provided to heat the outside air to room temperature during the heating season.
This problem has typically been solved by installing gas, oil or electric heaters and air-moving fans to heat the air within the buildings. When solar panels are used to heat a building, air is recirculated from the building through the collector and back. During the heating season, the ambient temperature is lower than the room temperature, and therefore a recirculating solar collector operates at a much reduced efficiency level.
Canadian Patent No. 1,196,825, issued Oct. 4, 1985 teaches the use of fresh make-up air for ventilation purposes, rather than simply recirculating interior air from a building. Using this method, the fresh make-up air is pre-heated by passing the air through a solar collector prior to introduction into the building. A glazing is provided over the solar collector, to provide a space between the two, through which the air is passed for heating. While this particular arrangement reduces the need for the use of consumable energy, the use of the glazing increases costs significantly. Advantageously, the glazing reduces radiation heat loss and negative wind effects. However, the amount of sunlight that is transmitted through the glazing is reduced to only about 85% of the sunlight. The use of a conventional glazed panel suffers other disadvantages including the requirement that the glazed panels be sealed. This again adds to the cost of the panels. Alternatively, if the glazed panels are used for heating fresh air, dirt and dust builds up in the panels and particularly on the underside of the glazing and there is no simple cleaning method. Therefore the panels must be designed for cleaning at regular intervals.
Canadian Patent No. 1,326,619, issued Feb. 1, 1994 and U.S. Pat. Nos. 4,899,728 and 4,934,338, issued Feb. 13, 1990 and Jun. 19, 1990, respectively, disclose the use of a solar panel that does not include a glazing, to heat fresh make-up air prior to introduction into a building. These systems are very efficient when heating large volumes of air per surface area of solar panel (i.e. ˜6 cubic feet per minute). This efficiency drops dramatically when lower air flow rates are used, however. Using low flow rates results in higher temperatures on the solar panel, leading to increased radiation heat loss to ambient. These systems also suffer other disadvantages. For example, the maximum temperature rise that is realized is approximately 30° C. over ambient temperature, for low flow designs. Clearly, this temperature rise is not sufficient in cold climate use. Also, the efficiency is greatly reduced on windy days as the wind blows heat away around the air inlets if the velocity of the air entering the panels is not great enough. Thus, these panels are best used on, for example, a south-facing wall, and are not as effective when used on a roof, due to increased wind velocities on a roof top. This is undesirable as the roof is a preferred position for solar panels for many people.
It is desirable to provide an apparatus for pre-heating ventilation air for a building that obviates or mitigates at least some of the disadvantages of the prior art.